并联机器人原文

Virtual Prototyping of a Parallel Robot actuated by Servo-Pneumatic Drives using ADAMS/Controls

Walter Kuhlbusch, Dr. Rüdiger Neumann, Festo AG & Co., Germany

Summary

Advanced pneumatic drives for servo-pneumatic positioning allow for new generations of handlings and robots. Especially parallel robots actuated by

servo-pneumatic drives allow the realization of very fast pick and place tasks in 3-D space. The design of those machines requires a virtual prototyping method called the mechatronic design [ 1]. The most suitable software tools are ADAMS for mechanics and Matlab/Simulink for drives and controllers. To analyze the overall behavior the co-simulation using ADAMS/Controls is applied. The combination of these powerful simulation tools guarantees a fast and effective design of new machines.

1. Introduction

Festo is a supplier for pneumatic components and controls in industrial utilization of pneumatic drives is wide spread in industry when working in open loop control. It’s limited however, when it com es to multipoint movement or path control. The development has been driven to servo-pneumatic drives that include closed loop control. Festo servo-pneumatic axes are quite accurate, thus they can be employed as drives for sophisticated tasks in robotics. The special advantage of these drives is the low initial cost in comparison to electrical and hydraulic drive systems. Servo-pneumatic driven parallel robots are new systems with high potentials in applications. The dynamical performance meets the increasing requirements to reduce the cycle times.

One goal is the creation and optimization of pneumatic driven multi-axes robots. This allows us to support our customers, and of course to create new standard handlings and robots (Fig. 1).

The complexity of parallel robots requires the use of virtual prototyping methods.

Fig. 1. Prototypes of servo-pneumatic driven multi-axes machines Preferred applications are fast multipoint positioning tasks in 3-D space. Free programmable stops allow a flexible employment of the machine. The point to point (ptp) accuracy is about 0.5 mm. The continuous path control guarantees collision

free movement along a trajectory.

. Why parallel robots

The main benefits using parallel instead of serial kinematics is shown in Fig. 2.

Fig. 2. Benefits of robots with parallel kinematics

High dynamical performance is achieved due to the low moved masses. While in serial robots the first axis has to move all the following axes, the axes of a parallel robot can share the mass of the workpiece. Furthermore serial axes are stressed by torques and bending moments which reduces the stiffness. Due to the closed kinematics the movements of parallel robots are vibration free for which the accuracy is improved. Finally the modular concept allows a cost-effective production of the mechanical parts. On the other hand there is the higher expense related to the control.

. Why Pneumatic Drives

The advantages of servo-pneumatic drives are:

direct drives→high accelerating power

compact (especially rodless cylinders with integrated guidance)

robust and reliable

cost-effective

Direct drives imply a high acceleration power due to the low equivalent mass in relation to the drive force. With pneumatic drives the relationship is particularly favorable. Festo has already built up some system solutions, predominantly parallel robots (see Fig. 1), to demonstrate the technical potential of servo-pneumatics. Which performance can be reached is shown in Fig. 3. This prototype is equipped with an advanced model based controller that makes use of the computed torque method [ 3].